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  #1  
Old 09-22-2008, 05:08 PM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
Posts: 41
Changed sparkplugs - Now BAD misfire

I could use some help here. I just changed the spark plugs in my 1994 Mercedes Benz E320. W124.

After putting the new ones in (autolite resistor replacing other resistor plugs), and securing everything, I started the car and had a very bad misfire. I went back in and changed the spark plugs back to the ones I took out, and still the misfire.

I picked up a new set of Bosch plug wires and boots for all six cylinders. Also, got another set of new plugs (NGK Platinums.) No difference.

I unplugged and re-plugged the two connectors associated with the intake ductwork several times to assure a good connection.

The car was running fine before I did the spark plug change. What in the world did I do? Can anyone make some educated guesses?

Mark

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  #2  
Old 09-22-2008, 05:22 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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..asumming you changed the connectors under each coil, I would say you have a bad wire harness.
Search "Wire Harness..."

,,,and the last thing you want in a 104 HFM system is Plats...
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  #3  
Old 09-22-2008, 05:30 PM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
Posts: 41
Okay, so you think that the disturbance to the old wiring harness caused it to fail somewhere? Any likely trouble spots?
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  #4  
Old 09-22-2008, 05:36 PM
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Location: Florida / N.H.
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Do the search..there are enough pictures in there to fill a NY City phone book.
I would cut it open where the feed to the coils junction.

And make sure you have the mapping correct
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  #5  
Old 09-22-2008, 08:43 PM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
Posts: 41
Right where the coil wires pass through the side of the dust cap over the plugs and coils, they are encased in the rubber insulator that fits along the edge. That's where I found the breach. As I dug into it a bit, I saw exposed copper wire. I took a utility knife and cut back towards the wiring harness to reach the end of the exposed wire.
Uh oh... So far, I've cut back around the back of the head, and still no end in site to the burned cracked insulation around ALL the individual wires. Going the other way, I've slit open the rubber housing and found the green oxidation eating its way throughout.

I've run out of electrical tape! I had to shore up the big bundle, or it would have crumbled under the handling. I can't imagine how it was running at all. Only due to being encased so tightly in the friction tape.

The challenge will be in seeing if I can get it to run long enough to get me to work for a couple of days. It doesn't look good.

Thanks for the help.
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  #6  
Old 09-22-2008, 09:18 PM
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You're past the point of having any reliability - could become undriveable at any point. There haven't been a lot of fires but I would carry a fire extinguisher if you do drive it.
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  #7  
Old 09-22-2008, 09:54 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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Unfortunately, there is only ONE fix.........and it is costly , too.....
But if the car is nice , it's worth the new harness.
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  #8  
Old 09-22-2008, 10:00 PM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
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I love my car.
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  #9  
Old 09-22-2008, 10:09 PM
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Location: Florida / N.H.
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Get one from Manchester...No Tax.
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  #10  
Old 09-22-2008, 10:12 PM
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Hold on skippy, check the diagram that shows the relationship between the 3 coils and the aother plug that each feeds and make sure you have everthing the way it should be, bt,dt.
Gilly
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  #11  
Old 09-22-2008, 10:22 PM
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He has already cut open the harness and found the problem insulation.
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  #12  
Old 09-22-2008, 10:33 PM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
Posts: 41
Sad, but true. In fact, the car is outside right now with a glow from the droplights spilling out into the night from under the hood. It's cold up here in New England tonight!

And I still gotta go out there and figure out how to get it to work in morning!

Later...
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  #13  
Old 10-15-2008, 11:10 AM
Mark
 
Join Date: Apr 2008
Location: Massachusetts
Posts: 41
Spark plug change and wiring harness resolved.

Thanks for all the help on this. It was about three weeks ago that I made the fateful decision to change the sparkplugs on my '94 e320. Replacing the wiring harness did indeed solve the problem.

The worst part - the price. With an employee discount at my company, I was able to get the engine harness for about $800 including Massachusetts sales tax.

The best part - The job is a snap. Three and a half hours for a complete novice (on wiring harnesses). All the existing plug receivers were clean, and there were no challenges. In fairness, I did get a little help from a friend who traced the second half of the job, while I was doing the part from the computer to the cam sensors.

One note: All of the original wire ties open and reclose, so don't haul off and snip them (like I did on the first one).

Other than that, there wasn't even a tricky part of the job, other than to say that at it's terminous, the plastic cover to the final plug needs to be studied to figure out how to unsnap it on the fender side. That's just like these kind of jobs. One pesky, unbelievably simple thing at the very end holds you up for what seems like an eternity, but in actuality was probably only five minutes.

There are two different engine harnesses for the '94 e320. One has a different plug shape at the thermostat housing. Be sure to provide your VIN number when ordering.

Car runs great.

Mark

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